Gurps Vehicles / 4th. Edition

[Thomson]

Originally Posted by Varyon

Fixing these problems isn't too difficult...

Well you basically rewrote the entire Gun Design System, but indeed the figures seem to fit pretty well.

[Varyon]

Originally Posted by Thomson

Well you basically rewrote the entire Gun Design System, but indeed the figures seem to fit pretty well.

I changed a value based on set barrel lengths to one that allowed for a range (but still scales the same way), and a value based on set calibers to one that allowed for a range (but still scales the same way). I also moved some numbers around to make things be in Imperial rather than metric units, as GURPS uses the former more than the latter. It's just higher resolution, not an outright rewrite. I'll admit Range and Acc use completely new methods, however. All that said, just using Vehicles as-is will still get you pretty close to the correct values, maybe using Acc/2 for smallarms and Acc/3 for larger weapons. Sure, damage, range and weight are going to be a bit off, but they'll still be in the right ballpark.

[kreios]

Originally Posted by Varyon

snip

Extremely interesting, and I'd be very interesting in the rest of your thoughts. I especially like the barrel length change.

One comment, though: Power and barrel length do indeed have an influence on the range (less power means less muzzle velocity, less barrel length means less efficient combustion). I've tested it with

1/2d range = 12.5 * calibre ^ 0.5 * barrel_length ^ 0.75 * power * T

where T is the TL factor, calibre is in mm (not in inches!), and barrel length in multiples of calibre.

range = 1/2d ^0.5 * 120 + 1/2d

indirect_range = 2.5*range

are as in Vehicles. From what I've tested, the numbers fit extremely well to a number of WWI and WWII artillery.

[Varyon]

Originally Posted by kreios

One comment, though: Power and barrel length do indeed have an influence on the range (less power means less muzzle velocity, less barrel length means less efficient combustion).

From what I understand, initial velocity doesn't actually matter when determining how far the bullet will be when it does half damage. This is because, while a higher speed means less time to travel a given distance, it also means a lot more air resistance slowing you down. This means it takes less time to cut your speed in half (or whatever half GURPS damage corresponds to), but you travel further per unit time, and apparently (this based on comments from user Anthony) it roughly works out that, for a given bullet design, size, weight, and orientation, it will reach 1/2D at exactly the same range, regardless of if it get there in half a second (high speed) or 3 seconds (low speed). Max is going to be influenced by velocity, as it's "how far will the bullet travel before it hits the ground," and a higher velocity means traveling further before this happens, but as engagements are rarely going to be anywhere close to Max, I'm fine with just winging it.

That said, if you have an equation that ends up giving you good agreement with historical results, use that. In fact, I may end up stealing that equation for my own use. I'm assuming the T variable uses the same values as in Vehicles, correct?

[Refplace]

Originally Posted by Varyon

From what I understand, initial velocity doesn't actually matter when determining how far the bullet will be when it does half damage.

The medium has an influience here as subsonic bullets travel farther in water and with more power than supersonic. At least according to a Myth Busters test.

[Varyon]

Originally Posted by Refplace

The medium has an influience here as subsonic bullets travel farther in water and with more power than supersonic. At least according to a Myth Busters test.

I originally had a note that things might change if you cross between supersonic and subsonic on your way down to 1/2D, but took it out because I wasn't certain.

I didn't think to specify that I was assuming Earth atmosphere at 1 atm pressure and typical Earth temperatures, but deviating too much in one of those directions is of course going to change things (it should go without saying that a bullet loses 1/2 its damage at a much more rapid rate when going through steel or flesh than air, for example).

[Refplace]

Originally Posted by Varyon

I originally had a note that things might change if you cross between supersonic and subsonic on your way down to 1/2D, but took it out because I wasn't certain.

I didn't think to specify that I was assuming Earth atmosphere at 1 atm pressure and typical Earth temperatures, but deviating too much in one of those directions is of course going to change things (it should go without saying that a bullet loses 1/2 its damage at a much more rapid rate when going through steel or flesh than air, for example).

As differing atmospheres and mediums (or lack of one) can affect things I would leave it as a minor footnote and ignore it for most things. Unless there was a good simple way to add it to the formula and I suspect it would not be a simple modifier. Nor to have to bother with varying densities in game. I only brought it up because it was such a dramatic difference and it was vaguely relevant and fun.

[kreios]

Originally Posted by Varyon

From what I understand, initial velocity doesn't actually matter when determining how far the bullet will be when it does half damage. This is because, while a higher speed means less time to travel a given distance, it also means a lot more air resistance slowing you down. This means it takes less time to cut your speed in half (or whatever half GURPS damage corresponds to), but you travel further per unit time, and apparently (this based on comments from user Anthony) it roughly works out that, for a given bullet design, size, weight, and orientation, it will reach 1/2D at exactly the same range, regardless of if it get there in half a second (high speed) or 3 seconds (low speed). Max is going to be influenced by velocity, as it's "how far will the bullet travel before it hits the ground," and a higher velocity means traveling further before this happens

"This can't be. A faster bullet should take far more distance to shed the additional velocity" - that was my first thought. However, it turns out that's actually true - the same bullet takes the same distance to halve its speed, no matter its initial velocity. Astounding, and something newly-learned!

That being said, the indirect firing range using the old formula still seems to work well, so I'm using your formula for 1/2d range, and the old one for max and indirect fire range.

but as engagements are rarely going to be anywhere close to Max, I'm fine with just winging it.

In my case, it's looking at artillery guns, so max range (or rather indirect fire range) is actually quite important.

That said, if you have an equation that ends up giving you good agreement with historical results, use that. In fact, I may end up stealing that equation for my own use. I'm assuming the T variable uses the same values as in Vehicles, correct?

Exactly.

[wellspring]

Originally Posted by Thomson

I did not write this to criticize your system. What I meant that if you have good reliable sources about real world vehicles written by experts on the field, you can just use them. In fact, that is less work.

Very true. I was working from the perspective of a situation where you wanted to create and use a construction system. If you're modeling existing ships and have their capabilities mapped out in GURPS terms, then yeah you just go ahead and use those.

[Thomson]

After skimming through Pyramid 3/34 and Spaceships 7 I found a lot of interesting stuff in there.